The use of solutions of polymer notably of polyacrylamide is known within the scope of assisted recovery of hydrocarbons contained in an underground formation (EOR, Enhanced Oil Recovery). Thus, after the operations for recovering hydrocarbons by means of the natural pressure of the deposit, a so-called “primary” deposit, it is generally preceded with a so-called “secondary” recovery of hydrocarbons, during which a solution of polymer is injected into the underground formation through injection well(s), and a mixture of hydrocarbons and of polymer solution is extracted from production well(s). The use of a polymer solution and not of water is preferred because of the often too great mobility of water: the flooding efficiency is improved by adding polymer to the injection water, as well as the production conditions (reduced percentage of produced water). A larger recovery rate is thereby obtained from the moment when it is decided to stop production (because of a too high percentage of produced water).
When several injection wells are used, it is generally necessary to operate at different pressures depending on the wells, in order to adapt to the local configuration of the underground formation, and to correct the heterogeneity effects of said underground formation. Now, several injection wells (or all the injection wells) are generally supplied with fluid by a same source of polymer solution. It is therefore necessary to have flow rate control valves for each injection well, notably within the scope of marine exploitation (offshore), where it would be too complex or too expensive to provide a supply line and one pump per injection well.
Among the flow rate control valves available for the above application, the company Cameron Willis proposes a model which consists in a cage pierced with holes. The inflow for the fluid is achieved on the periphery of the cage, and the outflow is at the centre of the cage. The accessible surface area for the fluid inflow is adjusted by a mobile piston which moves parallel to the axis of the cage. For a given flow rate, the pressure loss increases when the surface area accessible to the inflow of the fluid decreases. However, this system leads to a strong degradation of the polymer solutions used for assisted recovery of hydrocarbons, and therefore to a decrease in the viscosity of these solutions, which is strongly detrimental to their efficiency.
Moreover, U.S. Pat. No. 4,510,993 describes a flow rate control valve for polymer solutions, in which the flow rate is regulated by a needle penetrating into an orifice. The document indicates that the polymers are not degraded as long as the flow rate does not exceed 30 gallons/min, i.e. 7 m3/h. However, it is known that such a geometry (of the needle valve type) is degrading. Thus, the degradation of the polymer solutions in this type of system becomes high at more realistic flow rates of the order of 100 m3/h. Further such a system has significant risks of mechanical wear.
U.S. Pat. No. 3,477,467 describes a suitable flow rate control valve for a polymer solution, in which the pressure loss is obtained by having the polymer solution pass in a vertical tube filled with sands or beads. The adjustment of the amount of sand or beads allows regulation of the flow rate. However, this system also has the drawback of degrading the polymer solutions, and it also has significant risks of mechanical wear of the valve and of damage to the porous medium over time. Further, implementation is difficult.
U.S. Pat. No. 4,617,991 proposes a flow rate control system comprising a device actuated by the transport of a polymer solution, such as a hydraulic pump or a motor. This type of device is adapted for recovering the energy from the flow of the polymer solution. With the system, it is possible to avoid degradation of a polymer solution at a low flow rate (at most about 1.3 m3/h). However, it does not give the possibility of avoiding the degradation phenomenon at a higher flow rate. Actually, although the energy is dissipated outside rather than inside the pipe, the degradation remains a function of the geometry of the dissipation system inside the pipe.
U.S. Pat. No. 4,276,904 describes an apparatus with which a fluid flow rate may be modified by having the fluid pass into a limited number of tubes of different lengths and of different diameters. The pressure loss is adjusted by having the fluid pass in one of the combinations among the different tubes. This system is bulky, difficult to apply (the apparatus notably comprises a large number of valves, which have to be activated independently, at the outlet of each of the tubes) and not very flexible (i.e., with it, fine adjustment of the pressure loss and of the flow rate is possible only with difficulty). Such a system does not give the possibility of generating a sufficient pressure loss at a high flow rate.
Therefore, there exists a real need for development of a flow rate control valve adapted for the injection of polymer solutions in an underground formation which does not have the drawbacks mentioned above. In particular, a need exists for developing a flow rate control valve which does not induce any significant degradation of the solutions of polymer used within the scope of assisted recovery of hydrocarbons, even at a high flow rate.